The present invention relates to antennas and, more specifically to double monopole meanderline loaded antennas.
In the past, efficient antennas have typically required structures with minimum dimensions on the order of a quarter wavelength of the lowest operating frequency. These dimensions allowed the antenna to be excited easily and to be operated at or near resonance, limiting the energy dissipated in impedance losses and maximizing the transmitted energy. However, such antennas tended to be large in size at the resonant wavelength, and especially so at lower frequencies.
In order to address the shortcomings of traditional antenna design and functionality, the meanderline loaded antenna (MLA) was developed. U.S Pat. Nos. 5,790,080 and 6,313,716 each disclose meanderline loaded antennas. Both of these patents are hereby incorporated by reference in their entirety.
Generally, an MLA (also known as a xe2x80x9cvariable impedance transmission linexe2x80x9d or VITL antenna) is made up of a number of vertical sections and horizontal sections. The vertical and horizontal sections are separated by gaps. Meanderlines are connected between at least one of the vertical and horizontal sections at the corresponding gaps. A meanderline is designed to adjust the electrical (i.e., resonant) length of the antenna, and is made up of alternating high and low impedance sections. By switching lengths of the meanderline in or out of the circuit, time delay and phase adjustment can be readily accomplished.
Such a switchable meanderline allows the antennas to have a very wide tunable bandwidth. However, the bandwidth available for simultaneous or instantaneous use can be relatively limited in certain applications, such as multi-band or multi-use applications, or those where signals can appear unexpectedly over a wide frequency range. Examples of wideband MLA configurations are discussed in U.S. Pat. No. 6,323,814, which is herein incorporated by reference. For instance, an opposed pair of MLAs are adapted to operate in the monopole or vertical polarization mode relative to aground. In another configuration, two opposed pairs of MLAs sharing a common ground plane form a quad antenna.
These wideband MLA configurations provide a monopole mode, but require two or more feeds. Such multiple feed configurations typically require the use of supporting circuitry, such as 4-to-1 combiner circuitry in the case of a quad configuration. A wideband monopole MLA having a single feed may be desirable given the growing need for wideband antennas used in systems such as wireless and satellite applications (e.g., GPS and cellular telephone platforms).
What is needed, therefore, is a wideband monopole MLA having a single feed.
One embodiment of the present invention provides a double monopole meanderline loaded antenna. The antenna includes a horizontal reference plane, a pair of horizontal radiators, and a vertical radiator. Each horizontal radiator has an edge, and the edges are spatially located near each other thereby defining a gap. The vertical radiator is adapted to receive a single feed, and has a first end that is operatively coupled to the reference plane, and a second end located proximate the gap. The antenna further includes a pair of equalizing delay lines. Each equalizing delay line has a first end connected proximate the edge of one horizontal radiator, and a second end connected proximate the second end of the vertical radiator. In addition, each equalizing delay line has a low impedance section and a high impedance section relative to the corresponding horizontal radiator. The equalizing delay lines can be manipulated to equalize reactance of the antenna.
Alternatively, each equalizing delay line has its first end operatively coupled proximate the edge of one horizontal radiator and its second end operatively coupled to the ground plane (as opposed to the horizontal radiator). In this embodiment, each equalizing delay line has a low impedance section that is substantially parallel to its corresponding horizontal radiator, and a high impedance section that is capacitively coupled to the vertical radiator.
Another embodiment of the present invention provides a method of manufacturing a double monopole meanderline loaded antenna. The method includes providing a horizontal reference plane, and providing a pair of horizontal radiators. Each horizontal radiator has an edge wherein the edges are spatially located near each other thereby defining a gap. The method further includes providing a vertical radiator adapted to receive a single feed. The vertical radiator has a first end that is operatively coupled to the reference plane, and a second end located proximate the gap. The method proceeds with providing a pair of equalizing delay lines. Each equalizing delay line has a first end that is operatively coupled proximate the edge of one horizontal radiator and a second end that is operatively coupled to the reference plane. Alternatively, each second end is operatively coupled proximate the second end of the vertical radiator. In either case, each equalizing delay line has a low impedance section and a high impedance section, and the equalizing delay lines are adapted for manipulation during a tuning process to equalize reactance of the antenna.